This invention relates to a circular knitting machine of the cylinder and dial type, in particular for knitting hosiery.
More specifically, the invention concerns a circular knitting machine, wherein the needle cylinder and the dial are made rotatively rigid together through a coupling means located within the cylinder, said means comprising a rod coaxial with the cylinder and dial and rotatively connected to the dial, as well as rotatively engageable and disengageable with/from the cylinder, said means being shaped to allow the discharge of the knitted fabric when said rod is at least partly disengaged from the cylinder.
A machine of this general type is described in U.K. Published Application No. 2,035,390 A to Costruzioni Meccaniche Lonati S.p.A, corresponding to U.S. Pat. No. 4,339,932 to Francesco Lonati. In the latter machine, the rod extends through the whole needle cylinder up to a point beyond the bottom end thereof, and for cylinder engaging/disengaging, a rotary sleeve element is provided below the cylinder, the sleeve element being axially movable relatively to the needle cylinder and also having a means operative to engage with a matching means respectively provided on the rod. The axial displacement of the sleeve element, which is accomplished by means of a lever located on the machine outside, e.g. one controlled by the machine own program, involves mutual engagement or disengagement of the cylinder and dial.
The knitted fabric, upon completion, is discharged after the connection between the sleeve element and rod has been released. The knitted fabric discharge may be effected in two stages, namely by first bringing the fabric into the sleeve element and maintaining the rotary connection between the sleeve element and rod at the bottom end of the sleeve element, and then releasing this connection to simultaneously establish a connection at the top end of the sleeve element, whereby the fabric is allowed to drop out or be sucked out of the sleeve element; alternatively, the sleeve element may be simply disengaged from the rod in one step, such as to create a direct pathway for fabric discharging. In the latter case, the dial would be rotatively disengaged from the cylinder as the knitted fabric is being discharged, but this has no influence on the fabric because it would be already released from the needles. Upon re-establishing the connection, suitable indices on the sleeve element and rod would ensure the resetting of the exact cylinder to dial angular relationship.
In a machine of this type, therefore, the dial is no longer rotated through gears of its own to be driven by the machine main drive, but rather through the cylinder. Thus, a constant angular relationship is maintained between the cylinder and dial during rotation which cannot be always obtained with conventional machines, owing to the gear teeth being liable to wear rapidly, such that after a time an accurate alignment of the dial needles and cylinder needles can no longer be ensured, with obvious attendant defects in the knitted fabric.
A further advantage of a circular knitting machine of this type is the simplified construction of the portion overlying the dial, wherein it is no longer necessary to provide any rotary drive members.
By constrast, a machine of this type, particularly in the embodiment thereof which provides for a two-stage discharge of the fabric, has proved to be more complex internally at the portion underlying the cylinder, and owing to the need to operate the fabric discharge step simultaneously with mechanical operations in addition to the traditional knitwork sucking out step.